This invention relates to an adjusting mechanism for a pressure control assembly, and more particularly to an adjustable device which may vary the lever arm of a Belleville washer in a pressure control assembly.
The operation of a pressure control should provide for the accurate and positive actuation and de-actuation of an electrical switch at desired pressure differentials. To accomplish this, Belleville washers have been used in pressure controls because of their positive and effective snap action. However, the use of Belleville washers has not been totally satisfactory because of inherent manufacturing tolerances that result in varying spring rates for individual Belleville washers. A series of Belleville washers may be manufactured from the same batch of raw materials, using the same process, and heat set in the same manner, and yet each may not snap at precisely the same pressure as the next due to these inherent manufacturing tolerances. Slight variations in the thickness or height of each Belleville washer, may produce vastly varying snap pressures. The problem of compensating for the manufacturing tolerances in the spring rate of a Belleville washer in a pressure control is commonly encountered when designing a control for a particular application. Therefore, it would be desirable to have a mechanism that would correct for such tolerances, and improve the overall accuracy of a pressure control.
These types of manufacturing tolerances are also found in other springs, such as coil springs, used in combination with a Belleville washer in pressure control assemblies. Thus, an additional problem encountered is that the spring rates for the Belleville washer and the other springs in the assembly must be properly balanced so as to accurately determine the point of snapover for the Belleville washer.
Prior art attempts to correct for such tolerances and accurately calibrate a snap-acting diaphragm are described in U.S. Pat. No. 3,584,168 issued June 8, 1971, to Halpert for a "Fluid Pressure Operated Diaphragm Switch With Improved Means and Method for Calibration," and U.S. Pat. No. 3,816,685 issued June 11, 1974, to Fiore for a "Pressure Responsive Device Having Improved Means for Calibration." These methods use a calibration plate located beneath the diaphragm to pre-set the actuation and de-actuation pressure for the snap-acting diaphragm by deforming the plate to a desired position. Another approach described in U.S. Pat. No. 3,302,269 issued Feb. 7, 1967, to Cooper for "Methods of Making Condition Responsive Devices," introduces controlled hydraulic fluid pressure to pre-form a diaphragm blank to the desired configuration. However, these attempts have not been entirely satisfactory.